Impact Load Factor (Falling / Suddenly Applied Load)
How much harder a dropped or suddenly applied load hits than its dead weight.
Example
You enter
- Falling weight W (lb) 1000
- Free-fall drop height h (in) 2
- Static deflection under W, delta_st (in) 0.1
You get
- Impact factor 7.403 x static
- Peak impact force 7403 lbf
Details, formula, and sources
n = 1 + sqrt(1 + 2h/delta_st), impact force = nW, from the weight W, the drop height h, and the static deflection delta_st the member shows under W applied slowly. A 1,000 lb load dropped just 2 in onto a member that sags 0.10 in hits with n = 7.4, 7,400 lbf; let it down with NO drop and the factor is still 2 (2,000 lbf) - why a load must never be dropped onto a slack sling or rigid stop, and why a shock lanyard or rope stretch (bigger delta_st) tames the peak. Elastic, no energy loss; plasticity, damping, and member mass are separate. A design aid; Roark and the engineer of record govern.
n = 1 + sqrt(1 + 2h/delta_st); impact force = n W; impact deflection = n delta_st. At h = 0, n = 2.
The energy-method impact factor n = 1 + sqrt(1 + 2h/delta_st) for a load dropped onto an elastic member (Roark's Formulas for Stress and Strain; standard mechanics of materials), by name.
The energy-method impact factor is a standard published mechanics result; the weight, drop height, and static deflection are the user's inputs.
Estimate. AHJ and licensed professional govern.
Field names used by the API: weight_lb, drop_height_in, static_deflection_in, impact_factor, impact_force_lbf
- Impact factor n = 1 + sqrt(1 + 2h/delta_st); n = 2 at h = 0 (suddenly applied)Roark / mechanics of materials
- Energy method elastic, no energy loss; all drop energy goes into elastic strainenergy conservation
- Scope plasticity, damping, member mass, and rope/sling dynamics are separatescope of this tile